This invention relates to aircraft navigation systems and in particular to area navigation systems.
Basically, the concept of area navigation includes the use of a wide variety of geographic reference points to establish a desired navigational route wherein the position of the aircraft is computed and command signals are generated that are representative of course corrections necessary to maintain the aircraft on the desired navigation route. The guidance paths that comprise the desired navigation route are not limited to flight paths which pass directly over radio navigation aids (navaids) but can include geographic landmarks such as cities, geographic references having a known location relative to a navaid, or even geographic references having no specific relation to radio navigation aids. Hence, in essence an area navigation system permits automatic navigation relative to a generalized coordinate system such as the lines of longitude and latitude.
Prior art area navigation systems vary greatly in structural complexity and system capability, ranging from a simple system that provides the capability of flying directly to a single geographic location having positional coordinates referenced to the location of an operating navaid to rather sophisticated systems in which a complex navigation route including many waypoints can be established prior to the departure of the aircraft.
The more sophisticated prior art area navigation systems include a programmable digital computer, a control display unit (CDU) for controlling the system and displaying data to the system operator, and may include a map display unit for the display of navigational information relative to a computer-generated map of a relevant geographic region. The programmable digital computer includes storage registers for storing the coordinates of geographic locations pertinent to the navigation route to be followed on any particular aircraft journey and includes an arithmetic unit for performing mathematical calculations.
In general, the computer is programmed to establish a desired navigation route prior to the departure of the aircraft. In a typical arrangement, the programming of the navigation system computer can be accomplished by operation of a keyboard and associated control switches located on the CDU, or can be accomplished by loading a complete navigation route directly into the storage registers of the navigational computer from an ancillary storage device. During the flight, the computer arithmetic unit calculates the position of the aircraft from input signals supplied by conventional aircraft navigation systems and calculates guidance control signals that are representative of the flight control necessary to maintain the aircraft on the desired navigation route. These control signals are displayed to the pilot for appropriate action and can also be coupled to an automatic flight control system for automatically flying the desired navigation route.
The use of a programmable digital computer within an area navigation system provides a great deal of system versatility. Since the computer is programmable, the system can facilitate the calculation and display of a wide variety of navigational data that is of value to the flight crew during various phases of the flight. For example, the position of the aircraft along the navigation path can be displayed along with the present attitude of the aircraft and various other information stored within the digital computer can be accessed to aid in planning changes in the navigation route. Further, programming capability permits the modification of the previously established navigation route, or the establishment of a completely new route whenever desired or necessary. For example, it is often advantageous to modify a navigation route so as to avoid a storm system. Additionally, changes in traffic density may cause an air traffic control center to direct an aircraft to a holding pattern or landing approach pattern other than that which has been previously programmed into the computer.
In prior art area navigation systems, the CDU's are arranged to serve as the sole or primary interface between the operator of the system and the system computer. Thus, the CDU must provide for the initial programming of the navigation computer, the inflight modification of a programmed navigation route, and for initiating system operation to provide any other desired features. Although a great deal of effort has centered about designing such a CDU so as to minimize the number of necessary controls and to simplify the operating procedure, prior art area navigation systems have considerable drawbacks in that system versatility has only been achieved by compromising the ease of operation. This compromise necessitates considerable training in order to operate the system and also requires the performance of fairly complex and time consuming tasks during time periods when the work load in performing other necessary flight duties is at a maximum. This is especially true of situations in which a change in the navigation route becomes necessary. For example, when flying under the jurisdiction of an air traffic control center, dense traffic patterns or ground conditions may cause the air traffic control center to order the crew to enter a holding pattern or divert to another destination for landing. During such times, each crew member generally has a number of duties to perform in order to monitor the operation of various aircraft systems and control the flight of the aircraft. Hence, the pilot may be forced to choose between navigating without the benefit of the area navigation system or diverting attention from other duties long enough to reprogram the area navigation system. Such a choice is undesirable since maximum safety is not achieved regardless of the decision that is made. Further, because of the additional work pressure during this time period, errors can be made if it is attempted to modify the navigation route. Such errors are not only detrimental to precise system operation, but may greatly increase the safety risk. Primarily because of the complex procedure required to operate the system, and the fact that other operational duties are often highest during the time period in which modification of the navigation route is required, such prior art area navigation systems have not been favorably received by flight crews.
Further in prior art systems, changes in the navigation route must often be executed in a particular operational sequence and the geographic reference points available for use in the new or modified navigation route have often been limited to those locations stored within the area navigation computer. Such limitations are undersirable from the standpoint of system versatility and also from the standpoint of the ease of operation. Additionally, during the modification of a navigation route wherein the modification includes several changes, the prior art area navigation systems generally alter the programmed path as each change is entered via the CDU. Thus, the operator of the system does not have an opportunity to observe and verify the complete modified route prior to the time at which the route is modified within the computer storage registers. Consequently, operator errors can easily go undetected.
Accordingly, it is an object of this invention to provide an area navigation system including means for rapidly and conveniently entering navigation information into the system to modify a previously established navigation route or establish a new navigation route.
It is another object of this invention to provide an area navigation system in which the operational work load and the probability of operator error are both decreased.
It is a further object of this invention to provide an area navigation system wherein a previously established navigation route is not modified within the system computer until all proposed changes are entered and the tentative new navigation route has been verified.